An ever increasing number of enzymes (and other proteins as well) are being characterized which contain more than one polypeptide chain per molecule. Many of these enzymes contain only a single type of polypeptide chain while others have been shown to contain more than one. One objective of this research is to answer in as much detail as possible the questions: 1. What is the arrangement of the subunits within the enzyme? 2. What is the functional significance of this arrangement? and 3. As the subunit arrangement of many more enzymes is deduced, will certain evolutionary principles become clearly established? Studies on the mechanism of self-assembly of bacteriophage f2 will serve as a simple model system to be extended to more complex viruses. The development of procedures to obtain "conformationally native", nucleic acid free, viral protein components may prove to be of practical interest for producing "safe antigens". Physical and chemical studies on the fibrinogen fibrin conversion will include as immediate objectives developing procedures to determine in as much detail as possible the inter-and intra-molecular spatial relationships of the three types of polypeptide chains.